net: dsa: b53: Extend platform data to include DSA ports

The b53 driver already defines and internally uses platform data to let the
glue drivers specify parameters such as the chip id.  What we were missing was
a way to tell the core DSA layer about the ports and their type.

Place a dsa_chip_data structure at the beginning of b53_platform_data for
dsa_register_switch() to access it. This does not require modifications to
b53_common.c which will pass platform_data trough.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>